1. Field of the Invention
The present invention relates to a variable capacity type pump used in a power steering apparatus for a motor vehicle or the like.
2. Description of the Related Art
Conventionally, a variable capacity type pump used in a power steering apparatus for a motor vehicle or the like, as shown in Japanese Patent Application Laid-Open (JP-A) No. 9-14155, has a structure which has a cam ring being eccentric with respect to a rotor arranged in a pump casing so as to be rotated, forms a pump chamber between a cam ring and an outer peripheral portion of the rotor, increases an eccentricity amount of the cam ring with respect to the rotor during low speed rotation of the pump, thereby increasing the capacity of the pump chamber and increasing the discharge amount of a working fluid, and reduces the eccentricity amount of the cam ring with respect to the rotor at a time of a high speed rotation of the pump, thereby reducing the capacity of the pump chamber and reducing the discharge amount of the working fluid.
In the conventional art mentioned above, in order to reduce the pressure pulsation of the variable capacity type vane pump, and the vibration and sound induced therefrom, spaces of two closed portions comprised of a first closed portion formed by closing a suction port and a discharge port at a bottom dead center and a second closed portion formed by closing the discharge port and the suction port at a top dead center, among the pump chamber surrounded by the cam ring and the rotor are both formed as a space surrounded by a concentric circle around the center of rotation of the rotor under a maximum eccentric condition of the cam ring (in other words, a dynamic radius of the vane is set to be constant). In the conventional art, since a distance between the rotor and the cam ring in the closed portion is constant, an over compression on the basis of a capacity change of the pump chamber is not generated, so that it is possible to prevent a pulsation phenomenon on the basis of moving apart of the vane.
In the conventional art, since the structure is made such that the distance between the rotor and the cam ring becomes constant (that is, concentric) in the closed portion during the maximum eccentricity of the cam ring when the pump rotates at a low speed, an inner periphery of the cam ring and an outer periphery of the rotor are not concentric when the eccentricity amount becomes small during high speed rotation, so that it is impossible to prevent the vane from moving apart, and a great pressure pulsation caused by an increase of leakage in a gap at a front end of the vane is generated. Further, in the conventional art, it is considered that the moving apart of the vane is caused by the over compression within the closed chamber. However, by right as described below, the moving apart of the vane is mainly caused by an offset load on the basis of an unbalance between pressures applied to a front surface and a back surface of the vane existing in the closed section.
In FIG. 14, under a state that a vane 2 received in a groove of a rotor 1 receives a force in a centrifugal direction by a back pressure Pd and a centrifugal force so as to be in contact with an inner periphery of a cam ring 3, and the vane 2 rotates together with a rotation of the rotor 1, in a suction section until one vane 2A reaches an end point of a suction port 4, since the same suction pressure is applied to a front surface and a back surface of the vane 2A, no offset load is applied in a circumferential direction, and the front end of the vane 2A is pressed to the inner periphery of the cam ring 3 due to the back pressure Pd and the centrifugal force and does not move apart from the inner periphery of the cam ring 3. When the vane 2 exists in a first closed section which is not yet connected to a start point of a discharge port 5 after the vane 2 further rotates together with the rotation of the rotor 1 and the vane 2A passes through the suction section, a high pressure in a side of the discharge port 5 and a low pressure in a side of the suction port 4 are respectively applied to the front surface of the vane 2A and the back surface thereof. The offset load is then applied to the vane 2A in a circumferential direction, the vane 2A is inclined in a root portion received within the groove of the rotor 1 so as to be caught thereon. The vane 2A can not be pressed against the inner periphery of the cam ring 3 even by the back pressure Pd and the centrifugal force so as to move apart from the inner periphery of the cam ring 3, whereby the great leakage mentioned above from the discharge port 5 to the suction port 4 is generated with passing through the front end gap of the vane moving apart therefrom. Further, in the second closed section, the same phenomenon is generated.
A detailed description will be given below of problems in the conventional art. In the conventional art, under the maximum eccentric state (during low speed rotation), the inner periphery of the cam ring in the first closed portion and the second closed portion is formed in the concentric circle with the center of rotation of the rotor. Accordingly, since the dynamic radius of the vane in the closed section is constant at a time of the low speed rotation, the moving apart of the vane is not generated (FIGS. 15A and 16A), whereby it is possible to prevent the great pressure pulsation from being generated due to the moving apart. However, under the minimum eccentric state (during high speed rotation), the inner periphery of the cam ring is not the concentric circle with the center of rotation of the rotor together with the first closed portion and the second closed portion, and when the vane is caught on due to the offset load on the basis of the unbalance of pressure between the front surface and the back surface, the front end of the vane moves apart from the inner surface of the cam ring and the great pressure pulsation is generated.
That is, FIGS. 15A and 15B show a motion of the vane front end in the first closed portion by setting an angle of rotation of the rotor to a horizontal axis and setting a dynamic radius corresponding to a protruding radius of the vane with respect to the center of rotation of the rotor to a vertical axis, in which a solid line relates to the cam ring corresponding to the concentric circle with the center of rotation of the rotor, and a broken line relates to the cam ring formed in a completed round shape. In this case, since the distance between the rotor and the cam ring is constant as expressed by a relation Ha=Hb=Hc in FIG. 17A during low speed rotation in the first closed portion in FIG. 15A, the moving apart of the vane is hard to be generated. Since the cam ring becomes in the minimum eccentric state and the distance between the rotor and the cam ring becomes short in a center (Hb) of the first closed portion and becomes long in both sides (Ha, Hc) thereof as shown in FIG. 17B, at a time of the high speed rotation in the first closed portion in FIG. 15B, the vane is pressed in a centripetal direction in the front half of the first closed portion so as not to move apart. In a rear half, since the dynamic radius becomes a positive incline (a positive slope), the eccentric load is applied to the vane and the vane is caught on, so that the vane moves apart.
FIGS. 16A and 16B show a motion of the vane front end in the second closed portion by setting an angle of rotation of the rotor to a horizontal axis and setting a dynamic radius corresponding to a protruding radius of the vane with respect to the center of rotation of the rotor to a vertical axis, in which a solid line relates to the cam ring corresponding to the concentric circle with the center of rotation of the rotor, and a broken line relates to the cam ring formed in a completed round shape. In this case, since the distance between the rotor and the cam ring is constant as expressed by a relation Hd=He=Hf in FIG. 17A during the low speed rotation in the first closed portion in FIG. 16A, it is hard to generate the moving apart of the vane. However, when the cam ring becomes the minimum eccentric state during high speed rotation, the distance between the rotor and the cam ring becomes long in a center (He) of the second closed portion and short in both sides (Hd, Hf) thereof as shown in FIG. 17B, so that the vane generates the moving apart in a front half of the second closed portion.
An object of the present invention is to prevent a vane from generating a moving apart around a wide range of a pump rotational speed, in other words, around a wide eccentric area of a cam ring, in a variable capacity type vane pump so as to reduce a pressure pulsation and a vibration and a sound generated together therewith.
The present invention relates to a variable capacity type pump comprised of a pump casing with a complete round rotor arranged therein so as to be rotated, and a cam ring set in the periphery of the rotor, forming a pump chamber with respect to an outer peripheral portion of the rotor and capable of being eccentric with respect to the rotor. A suction port is arranged in the pump casing and sucks a working fluid to the pump chamber, and a discharge port arranged in the pump casing and discharges the working fluid from the pump chamber. A plurality of vanes received in a groove of the rotor, protruding so as to freely move in a radial direction and in contact with an inner periphery of the cam ring at front ends and the working fluid sucked from the suction port is held in a space between the adjacent vanes. The working fluid is transferred due to a rotation of the rotor so as to be discharged from the discharge port. The amount discharge of the working fluid is increased by increasing an eccentric amount of the cam ring with respect to the rotor. The inner periphery of the cam ring is constituted by a shape of a suction section sucking the working fluid from the suction port, a shape of a first closed section at a bottom dead center transferring the working fluid sucked from the suction port to the discharge port after previously compressing, a shape of a discharge section discharging the working fluid from the discharge port, and a shape of a second closed section transferring the working fluid held in the space between the adjacent vanes at a top dead to the suction port.
The inner periphery of the cam ring in the suction section and the discharge section is constituted by a complete round curve and a transient curve. The inner periphery of the cam ring in the closed section is constituted by a negative slope curve in which a radius of curvature reduces along the rotational direction of the rotor so as to always reduce a dynamic radius of the vane with respect to an increase of the rotational angle of the rotor without relation to the eccentric amount of the cam ring.
The present invention relate to a variable capacity type pump comprised of a pump casing with a complete round rotor arranged therein so as to be rotated and a cam ring set in the periphery of the rotor, forming a pump chamber with respect to an outer peripheral portion of the rotor and capable of being eccentric with respect to the rotor. A suction port is arranged in the pump casing and sucks a working fluid to the pump chamber and a discharge port arranged in the pump casing and discharging the working fluid from the pump chamber. A plurality of vanes received in a groove of the rotor, protruding so as to freely move in a radial direction and in contact with an inner periphery of the cam ring at front ends and the working fluid sucked from the suction port is held in a space between the adjacent vanes, the working fluid being transferred due to a rotation of the rotor so as to be discharged from the discharge port. The amount of discharge of the working fluid is increased by increasing an eccentric amount of the cam ring with respect to the rotor. The inner periphery of the cam ring is constituted by a shape of a suction section sucking the working fluid from the suction port, a shape of a first closed section at a bottom dead center transferring the working fluid sucked from the suction port to the discharge port after previously compressing, a shape of a discharge section discharging the working fluid from the discharge port, and a shape of a second closed section transferring the working fluid held in the space between the adjacent vanes at a top dead to the suction port.
The inner periphery of the cam ring in the suction section and the discharge section is constituted by a complete round curve and a transient curve. The inner periphery of the cam ring in the closed section is constituted by a plurality of negative slope curves in which a radius of curvature reduces along the rotational direction of the rotor so as to always reduce a dynamic radius of the vane with respect to an increase of the rotational angle of the rotor without relation to the eccentric amount of the cam ring.